The traffic flowing into a network device—e.g., a router, switch, bridge, server, and the like—is generally made up of multiple abstraction layers (e.g., the Open Systems Interconnection (OSI) model). Each of these logical layers generally relates to communications functions of a similar nature. For instance, layer 2 of the OSI model is known as the data link layer and uses physical addressing (e.g., Media Access Control (MAC) addresses) for switching traffic. Layer 2 encapsulation generally provides the mechanism for transferring data between network entities, and can also be used for error correction for layer 1. As another example, layer 3 traffic is known as network layer traffic and uses logical addressing (e.g., Internet Protocol (IP) addresses) for routing traffic. Layer 3 encapsulation generally provides the mechanism for transmitting data between a source host on a first network to a destination host located on a second network.
Generally, routers can be configured to forward packets from one network to another. For instance, a router may receive a packet, inspect the IP address in the packet's header, and compare the IP address to route information stored in the router's internal routing table to determine what to do with the packet. For example, the router could determine a destination for the packet based on information in the router's internal routing table and could forward the packet on towards the destination. As the packet is switched from router to router, its IP address may remain the same, but its MAC address may be updated to the next router interface along the path.
Overlay Transport Virtualization (OTV) provides a solution to extend layer 2 connectivity across different sites using an existing layer 3 network. With OTV, layer 2 extensions across multiple data centers is achieved by configuring one or more OTV edge devices at each of the data centers to extend a set of virtual local area networks (VLANs) across the multiple data centers. By doing so, remote-site MAC addresses can be installed on the edge devices, such that hosts within a first one of the data centers can access hosts within the other data centers using layer 2 communications. As a result, these techniques can extend layer 2 connectivity across multiple different sites.